Fast-acting electromagnetic counting device



J. 1. BELLAMY 2,909,712 FAST-ACTING ELECTROMAGNETIC coUNTING DEVICE Oct. 20, 1959 Filed Dec. 13, 1955 United States Patent C) FAST-ACTING ELECTROMAGNETIC COUNTING DEVICE John I. VBellamy, Wheaton, Ill., assignor to International Telephone and Telegraph Corporation, New York, N.Y., a corporation of Maryland Application December 13, 1955, Serial No. 552,829

7 Claims. (Cl. S17-155.5)

v This invention relates to a fast-acting electromagnetic counting device. Its main object is to provide a device of this character which will operate reliably in response an operating path cause the armatures to respond in a counting succession and to be held operated residually, while a pulse transmitted to the electromagnet over a restoring path neutralizes the residual magnetism to permit the operated armatures to restore. The armatures are commonly used to actuate and restore respective sets of contacts. One embodiment of such a device is illustrated in United States Patent No. 2,538,818, while the pending United States patent application of Richard P. Arthur, Serial No. 256,888, liled November 17, 1951, now Patent No. 2,736,845, covers an improved form which has been widely used commercially. In the usual commercial form of the counting device, its electromagnet has two reversely connected windings, comprising an operating winding and a restoring winding. y

As used commercially, the electromagnetic counting device has had the limitations that (l) an operating Winding capable of causing the desired armature operation in response to short operating impulses oversaturates the magnetic structure in response to prolonged operating impulses, thereby rendering quite critical the adjustment of theV relatively small restraining air gap between the armatures and the pole face of the magnetic hold-back yoke, and that (2) a restoring winding capable of neu-v tralizing the residual holding ilux, but incapable of reoperating any of the restored armatures, actsso slowly that a restoring pulse must be longer in duration than a minimum operating pulse. apparatus often must include an additional relay, to open the restoring circuit after the counter has cleared out, for the often-suggested practice of opening therestoring circuit by contacts directly controlled by an operated armature (such as the rst) usually results in some of the other armatures remaining operated because the armatures vary somewhat as to the reduction in residual ilux required to permit them to restore, and the selected circuit-controlling armature is often one of the first to be released, whereupon it restores and opens the restoring circuit before the residual ux has been reduced enough to release the remaining armatures which have been operated.

According to the invention, the foregoing drawbacks are overcome by increasing the steady-state wattage of Moreover, the associated control Y2,909,712 Patented Oct. 20, 1959 ice high value (about fty watts in the selected example), and by employing only a relatively small number of turns on the electromagnet in either path. In either path, the turns are so related to the supply voltage that the ampereturn rise of current is rapid until its desired Value is reached, following which the opening of the circuit and/ or the development of current-resistance drop (IR drop) limits the developed ampere-turns to a Value which'is below oversaturation for the operate winding and is below reoperate value for the restoring winding.

A feature of the invention is that a restoring winding produced according to the stated procedure permits the contacts which open with the restoration of any de- Y siredvoperated armature to .be used to open the restoring circuit without opening it too soon, despite the existence of a critical zone (from about 52 to about 68 arnpere turns) extending from (l) the ampere-turn value at which the most lightly held operated armature is released for restoration to (2) the ampere-turn value atV which no operated armature can remain operated. The rise of restoring ampere-turns obtained by a restoring winding produced according to the invention is sufficiently rapid within the stated critical zone that such zone has a duration less than that required for an armature to restore, and open 'its contacts, upon being magnetically released for restoration.

The above-mentioned and other features and objects of this invention and the manner of attainingthem will become more apparent, and the invention itself will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings comprising Figs. l to 4, wherein:

Fig. 1 shows a signal system wherein they counting device of Figs. 3 and 4 is employed;

' Fig. 2 shows the graphic comparison of the restoring characteristics of the `new and improved electromagnet with the electromagnet heretofore used; and

Figs. 3 and 4 are respectively a top view and a side view of the improved counting device.

Figures 3 and 4 armatures A1 to A10 comprise the front limb; and elecboth the operating path and the restoring path to a rather tromagnet 2 and actuating pole member 3 comprise the lower limb.. Y

- As disclosed in the noted application, the single electromagnet 2 includes a relatively wide, at core 9, a rectangular rear spool head 10, and an oval front spool head 11, and a winding 12 wound between the spool heads. The rear spool head 10 is provided with winding terminals 14. Electromagnet 2 is secured to return plate 1 by a pair of screws 13.

L-shaped actuating pole member 3 is secured to the front pole face of core 9 by screws 28 (Fig. 4), which also retain the L-shaped non-magnetic armature-guide comb 27. Parts 18, 19, and 6 which form the restraining-pole branch are secured to the horizontal lower limb of pole member 3 by screws 20. Screws 24 secure the non-magnetic backstop comb 23 to the outside vertical face of member 6.

Each armature A1 to A10 has an opening for receiving pivot rod 31. Pivot rod 31 is held by each of the eleven curled-over teeth-like projections of the magnetic pivot 3 bracket 30, between which the ten armatures rest. Bracket 30 is held in place by counter-sunk screws 32 which pass through tapped openings in the bracket.

Contact-bank assembly 5, attached to return plate 1, supports ten similar contact sets C1 to C10, one for each of the ten armatures A1 to A10. This assembly includes parts clamped between plates 55 and 56 by short screws 50 as disclosed in the noted application. Bank assembly 5 underlaid by the controlled-spring assembly comprising layers of springs 44, 45 and spacers 58 clamped between plate 57 and return plate 1, by vsingle counter-sunk screw (not shown). The latter assembly is applied iirst and secured, following which the contact-bank assembly 5 is placed in a position over it and is secured by screws 51 which threadedly engage return plate 1. This construction permits the device to be adjusted for its desired sequential counting operation before the contact bank 5 is applied, and therefore while the control blades 44 and 45 are more accessible for individual corrective adjustment.

As best seen in Fig. 4, each contact stackup C1 to C10 comprises four contact blades 62 to 65, lower normally open pair (make combination) 64 and 65, and an upper, normally closed pair (break combination) 62.and 63. External connections to the contact blades may be made through their rear terminal portions 66. Each contact stackup has a cross-shaped actuating member 61 of insulating raterial secured between contact blades 62 and 65. The widened central portion of any part 61 passes freely through relatively wide longitudinal slots in stationary blades 63 and 64, and the upper and lower portion of any part 61 are received in the narrower longitudinal slots in traveling blades 62 and 65. As disclosed in the noted application, parts clamped between plates 55 and 56 includes a metal adjusting plate 79 (with adjusting ears 80) and insulating plates.

As explained in the noted application, the free end of the metallic adjusting plate 79 extends forwardly to terminate in the adjustment tabs 80 which rest on the ends of posts 33, which comprise reduced-diameter upward extensions of screws 32.

As seen in Fig. 4, the first armature A1 normally stands much nearer tothe face of the main tractive pole member 3 than do armatures A2 to A10, the latter standing against respective teeth of the non-magnetic backstop comb 23, and in tractive proximity to the face of the restraining pole member 6. As explained more fully in the noted application, these relatively normal positions are assumed because (l) each armature A1 to A10 has a lightly tensioned underlying lift spring 45, and (2) each armature except A1 is under the normal restoring force of the laterally offset tip` of an overlying spring 44 to restore it fully.

When the first pulse energization of electromagnet 2 occurs, the partly advanced armature A1 operates fully, in a clockwise direction as viewed in Fig. 4, until i-t engages main pole member 3, where it is held individually because of the magnetically hard nature of core 9 of the electromagnet.

On operating fully, armature A1, through its tail portion `41, raises the overlying offset control spring 44 thereby mechanically freeing the second armature A2 for preliminary movement out of the restraining influence of the hold-back pole member 6 to its intermediate position but that movement is delayed magnetically by member 6 until the instant impulse subsides, whereupon the preliminary movement of A2 occurs to mark the end of the first pulse and to condition the armature A2 to respond fully to the second pulse energization of electromagnet 2.

The remaining armatures operate similarly responsive respectively to successive pulses, resulting in the armatures operating successively, and remaining operated by residual magnetism.

A contact stackup of any operated armature A1 to A10 is actuated through its associated insulating stud 61 to open the upper contact pair and to close the lower.

The electromagnet 2, as shown diagrammatically in Fig. l, has two differentially connected windings. Operate winding OP receives impulses to be counted, the restoring winding R is for neutralizing the residual magnetism to permit the operated armatures to restore.

Figure 1 Fig. 1 illustrates the use of the device of Figs. 3 and 4, in a simple signalling system wherein residual magnetism is employed exclusively to hold the operated armatures.

In the system of Fig. l, the counting device is illustrated in circuit diagram within the rectangle labeled Counter" and a relay group controlling the operation of the system is shown within a further rectangle labeled Control Circuit. The impulse counter is controlled over line 100, through the illustrated control circuit, to light signal lamps S1 to S10 selectively. The control is exercised from one of the illustrated remote control stations ST1 or ST2. Apparatus included at station ST1 is a switch key SKI and a calling device CD1, of the usual telephone type, which can transmit a series containing from l to 10 break impulses. Station ST2 includes similar apparatus, a switch key SK2 and a calling device CD2. In the control circuit, relay 102 corresponds to the -line relay generally employed in automatic telephone systems; relay 103 corresponding to the slow-restoring release relay; relay 104 is the slowrestoring series relay which is operated before and during dialing, after which it is restored; and relay 101 is a differential relay having two differentially connected windings whereby it remains unoperated when balanced control is exercised from station ST1, but is operated when unbalanced control is exercised from station ST2, as will hereinafter bc described.

If the disclosed signalling system is employed as part of an exchange telephone system, the current-supply source (indicated in Fig. l by the ground symbols and by the supply terminals marked with a negative sign) may be the usual exchange battery, which is maintained yat or about fifty volts as marked for the terminal to the iight of electromagnet 2.

yIn the disclosed signalling system, both remote control stations (ST1 and ST2) can control the lighting of signal lamps S1 to S9 selectively but only station ST2 can cause signal lamp S10 to become lighted effectively, or more than momentarily.

Assume now that a desired one of the signal lamps S1 to S9 is to be lighted to display a corresponding signal from station ST1. This operation is eiected from the control station by iirst closing key SKll and manipulating the calling device CD1 to transmit the desired number of impulses over the line 100. Line relay 102 responds to `the closure of key SKI by operating release relay 103 and series relay 104-to prepare an impulse circuit for the counter. The operate circuit for series relay 104 includes contact blades 62 and 63 of contact set C1 of the counter. Being slow-restoring, release relay 103 and series relay 104 remain operated throughout the restoration of line relay i102 incident to the assumed operation of calling device CD1. Dilerential relay 101 does not operate upon the closure of key SKI because both of its windings are energized over a circuit from ground through its lower winding over the closed loopV circuit over line i100, its upper winding in series with line relay 102 to battery.

At its contacts 1, release relay =103 prepares a restoring path for Ythe restoring winding R of electromagnet 2; and at its contacts 3, it prepares to apply a ground potential to wire LP upon the resoration of relay 104; and at its contacts 2, it prepares an operate path for the counter through its winding OP, resistor 105, to battery.

operate sequentially, with results to be described hereinafter, K v

As previously stated, the steady-state wattage of the restoring path and of theoperating path of the disclosed counting device have both been considerably increased over the wattagek values previously used for these paths, and a reduction has been made in the number of turns usedfor the windings of electromagnet 2, which comprise operate-'winding OP and restoringwinding R. This turn reduction and wattage increase coact to greatly shorten the time required fory the desired action to occur following circuit closure. Beside allowing the use of a restoring winding that acts fast enough to permit its circuit to be safely opened on the release of any operated armature, and an operating winding which causes armature operation to occur responsive to shorter operating impulses, this provision permits the steady-sate ampere- `turns value of the operating winding to be greatly reduced. Thus much of the oversaturation formerly occurring on long operating impulses is avoided, as a consequence of which the mechanical adjustment is rendered less critical and the tolerable inter-impulse interval is rel duced, which is in addition `to the faster response.

When the counter hasthe physical structure shown in Figs. 3 and 4, wherein the magnetic return member 1 iS two inches in width, with the other dimensions in substantially the relative proportions shown, the minimum safe operating magnetomotive force has been found to be about 325 ampere turns; while about 52 ampere turns (at the lower limit of the critical zone previously referred to) is usually Isufiicient to restore one or more armatures (but never all), the minimum safe restoring magnetomotive force has been found to be about 68 ampere-turns, whichv is the upper limit of the said critical zone, and the maximum safe restoring magnetomotive force is found to be substantially in excess of 200 ampere turns. The illustrated structure exhibits a comparatively low magnetic reluctance to magnetomotive force developed in winding 12 of Fig. 4 (R and OP in Fig. l) compared to other small electromagnetic devices such as telephone relays. Consequently, any winding turn on electromagnet 2 exhibits a correspondingly high inductance, with a correspondingly high factor of back E.M.F., which is now found to require a correspondingly high applied per turn -during the interval kof current rise to either ampere-turn value indicated above if such value is to be reached with the contemplated promptness following circuit closure.v It is for this reason that, in carrying out the invention, it has been found necessary, as stated, to employ a considerably increased steady-state `wattage for both the operating path and the restoring path of the illustrated counter. A steady-state power consumption of fifty watts has been found satisfactory for either winding of the disclosed counter. This value permits employing a sutlcientlyhigh voltage per turn to either Winding (R or OP, Fig. l) that the ampereturn rise occasioned by excitation of the winding occurs with suicient rapidity that the required minimum ampere-turn value is reached lvery quickly. The resistance of the path (which is inversely related to the wattage for any given voltage) acts to set a limit on the steadystate current and ,thus on the steady-state wattage and on the ampere-turns of the Winding in the'closed path.

The foregoing principles are shown applied to the counter illustrated in circuit diagram in Fig. l by (1) employing a 50-chm resistor 105 in the common portion of the paths through respective windings OP and R of electromagnet 2; (2) providing winding OP in the form of 450 turns having negligible resistance (instead of the usual 1250 turns in a 33-watt, 50-volt path), across which the 50-volt current source applies one-ninth volt per turn at the instant of circuit closure, thus securing an initial high rate of liux change in the structure suilicient to induce a three-times-increased back voltage of oneninth volt per turn compared to the usual one-twentyfth volt per turn, with the 50-watt limit imposed by resistor limiting the steady-state current to one ampere, which gives a steady-state magnetomotive-force value to winding OP of 450 ampere turns, which is but little more than half the usual 833 ampere turns; and (3) providing Winding R in the form of 200 turns of negligible resistance (instead of the usual 2350 turns in a 3.6-watt, 50volt path), across which the SO-volt current source applies one-quarter volt per turn at the instant of circuit closure, thus securing an initial very high rate of ilux change in the structure sufficient to induce about twelve-times-increased back voltage of one-quarter volt per turn compared to the usual one-forty-seventh volt per turn, with the 50-watt limit imposed by resistor 105 limiting the current flow to one ampere, which gives a steady-state malgnetomotive force value to winding R of 200 ampere turns, which is a little more than the usual ampere turns but is still value.

Returning -now to the operation being described for Fig. l, upon each described circuit closure by relay 102 of the path through operate winding OP (through contacts of relays-102, 103, and contacts 1 of 104), current starts to ilow through winding OP and resistor 105, and rapidly reaches lthe value which excites winding OP at the stated operating value of 325 ampere turns. This value is quickly reached because the described relatively high inductance factor of winding OP is offset by the described high per-turn value of the applied E.M.F., which is initially one-ninth volt per turn. Tests indicate that the operating value is thus reached in less than three milliseconds in the disclosed example.

When the operate value is reached, the one of the armatures A1 to A10 'which is on-call (in its intermediate position) operates fully.

If the circuit closure is maintained after the above opcrate value is reached, the current continues to rise toward its steady-state, l-ampere, SO-watt value which excites the winding OP to a maximum of 450 ampere turns. Since 450 ampere turns is less than forty percent above kbelow the safe maximum the said minimum operate value of 325 ampere turns,

the tendency formerly experienced (at 833 ampere turns) toward oversaturation of restraining pole member 6 of Fig. 4 (to render very critical the adjustment of the teeth of non-magnetic gap-determining member 23) is so greatly reduced as to become a minor factor.

At the end of any operating impulse (upon reoperation of line relay 102), the consequent cessation of winding current leaves operative only the residual magnetomotive force of the mildly hard core member 9 (Fig. 4) to hold any operated armature by residual magnetism. At this point, the next armature in sequence is released by member 6 (Fig. 4) to move into its on-call, or intermediate, position where it is ready to obey `the next operating impulse. In this-manner, any desired number of the contact sets C1 to C10, controlled by armatures A1 Vtransmitted impulse series but restores and opens its maintaining circuit, the described operating path at its contacts 1, at the end of the series of operating impulses. Upon restoring, series relay 104 also grounds signal wire LP at its contacts 2, through contacts 3 of operated `release relay 103. The ground potential applied to wire LP is extended to the counter thereby completing a lighting circuit for one of the signal lamps S1 to S10, which corresponds to the last-operated one of contact sets C1 to C l If, for example, the received impulses in a series contains only a single impulse, only contact set C1 has been operated. In this event, lamp S1 is lighted in a circuit through the contact blades 62 and 63 of contact set C2 (contact blades 62 of contact sets C2 to C10 are strapped- Wired together), signal Wire LP, contacts 2 of relay l104, to ground through contacts 3 of release relay 103. On the other hand, if two impulses have been received, contact set C2 is operated along with contact set C1. The lamp S1 is disconnected (by the separation of contact blades 62 and 63 of contact set C2), and lamp S2 is substituted being connected to signal Wire LP by the noted strap wiring, Contact blade 63 of contact set C3, and contact blades 64 and v65 of contact set C2.

Operation of any succeeding contact set C3 to C9 results in the disconnection of the signal lamp associated with the preceding contact set and the substitution of the locally associated signal lamp.

When the system of Fig. l is to be cleared out, switch key 8K1 is opened, permitting line relay =102 and release relays 103 to restore. With relays 102 and 103 restored and armature A1 of the counter still operated a restoring path is completed for the counter from ground at back contacts of relay 102, Via back contact of contacts 2 of relay 103, contact blades 64 and 65 of contact set C1, the 200-turn demagnetizing, or restoring, winding R of electromagnet 2, resistor 105, to battery. As will be hereinafter described more particularly with the aid of Fig. 2, the current ow in this restoring path rises so quickly to a value which applies a reverse-)flux ampere-turn value at winding R in excess of the safe release -value (of about 68 ampere turns) that all operated ones of armatures A1 to A10 are reliably released magnetically before contact members 64 and 65 of C1 can be opened by the restoration of armature A1, even though armature A1 may become magnetically released upon the ampere-turn effect at R reaching a minimum of, for example, about 52 ampere turns, as hereinafter discussed. Resistor 105 limits the steady-state current through winding R to one ampere, in the assumed 50- Iwatt example, in the event that armature A1 mechanically binds or that contact set C-1 otherwise fails to restore.

When all operated armatures of the counter, and contact sets C1 to C10 have restored (usually within less than one millisecond), the system of Fig. l has been returned to its normal illustrated position.

As previously stated, station ST1 is unable to cause signal lamp S10 lto become lighted effectively. If an attempt is made to light control lamp S10 etfectively from station ST1, by actuating calling device CD1 to send a series of ten impulses over line 100, the counter responds to cause the armatures A1 to A10 to operate sequentially. The operation of armature A10 actuates its associated contact set C10 to prepare a restoring path for the counter which, upon the described restoration of series relay 104 places ground on LP, is completed from ground on wire LP, via lower contacts of contact set C10, jumper I, contacts 1 of operated release relay 103, contacts of the unoperated differential relay 101, restoring Iwinding R of electromagnet 2, resistance 105, to battery. Current ow through winding R of electromagnet 2 releases all of the operated armatures in the manner previously described, with the lower contact pair of contact set C10 opening the restoring path. Lamp S10 is thus disconnected after A8 y only a bare icker. Ulpon the restoration of contact set A1, the upper Contact pair thereof recloses the operate circuit for series relay 104, again conditioning the system for the receipt of impulses. Calling device CD1 may be reoperated to transmit series of impulses to the control circuit, orswitch SKl may be opened to restore relays 102 to 104.

Upon restoring, relay 102 transmits an incidental operating pulse through Winding OP, but this circuit is replaced by the described restoring circuit, and the counter is immediately restored, upon the restoration of relay 103. Relay 104 then res-tores to complete the clearout operation.

)If it is desired to restrict station ST1 from exercising control over some other signal lamps, for example S7, jumper I may be shifted from the associated contact blade of set C10 to the corresponding blade of C7 whereby the receipt of a series of seven impulses immediately restores the counter to its normal illustrated condition when series relay 104 restores.

As noted, the circuit also discloses an arrangement whereby control from station ST2 may be extended over line 100 to control any selected signal lamp S1 to S10 irrespective of any jumper J. This is accomplished by applying ground potential through resistor 106, contacts of switch key 8K2 to the line 100, thereby shunting the lower winding of differential relay 101, while energizing the upper winding thereof in series with line relay 102. The operation of differential relay 101 in series with relay 102 opens the restoring path for the counter which would normally include wire LP, contact blades 64 and 65 of contact set C10, and jumper I as described.

Opening switch key SK2 restores relays 101 to 103, thereby clearing out the apparatus as described for station ST1.

Figure 2 By curves A and B, respectively, Fig. 2 illustrates graphically, by a plot of magnetomotive force in ampere turns along the vertical axis against time in milliseconds along the horizontal axis, the time rate of increase of restoring magnetomotive force developed along curve A by the 20G-turn restoring winding R of Fig. 1 in the 50- volt, SO-Watt, restoring path there shown, in comparison with that developed along curve B by the usual 2350- turn restoring winding as heretofore used in a SO-volt, 3.6- watt restoring path.

Vertically, curves A and B cover the range from zero to slightly above ampere turns, which includes the previously noted critical zone between horizontal lines 201 and 202 (about 52 and 68 ampere turns) within which one or more armatures of the structure may be released magnetically, with at least one armature failing to be released.

Curve B dwells within the said critical zone, between points 205 and 206 (at about 1.125 and about 1.843 milliseconds, respectively) for about .718 millisecond. This dwell interval thus covers the major portion of a millisecond, which as experience has shown is substantially more than suicient time for any magnetically released armature to restore and to open the restoring circuit before all armatures have been released magnetically, provided the armature in question is one controlling the restoring circuit, as through contact set C1 or C10 of Fig. l.

Curve A dwells within the said critical zone between points 203 and 204 (at about .094 millisecond and .154 millisecond, respectively) for only about .06 millisecond, which is about one twelfth the amount of critical-zone dwell of curve B. This small critical-zone dwell is so iieeting that, once reached at point 203 the critical zone is passed at point 204 before any armature magnetically released Within the critical zone can restore and open its contacts. This characteristic renders feasible for the first time the self-opening restoring-circuit practice for a 9 residually held multi-armature device as disclosed in Fig. 1. y

The bending toward the horizontal of curves A and B, particularly noticeable above line 202, results from the progressive development of the so-called IR-drop voltage across the resistance of resistor- 105 (Fig. l) as the current rises toward its final steady-state value, at which the entire drop is across the resistance of the restoring path.

Ilf the device of Fig. 1 is to be operated from a higher or lower supply voltage, it will be understood that the number of turns at R and OP is increased or decreased correspondingly, to provide the stated respective voltages per turn on circuit closure, and the path resistance is increased or decreased to an extent necessary to maintain the steady-state value of the wattage of the paths. For example, if half-Voltage or 25-vo1t operation equivalent to the described 50-volt operation of Fig. 1 is desired, the turns at R and OP are halved, to 100 and 225 to provide an unchanged volts-per-turn, and the resistor 105 is quartered to 12.5 ohms to give a 50-watt steady-state consumption.

In practice, the resistance of the windings R and OP of Fig. 1 may not be negligible, in which case the resistance at 105 may be lowered correspondingly, and 105 may be tapped for separate terminations of the windings if desired. Separate resistors may be used for the windings, particularly if the control circuitry is such that both windings may be closed at the same time under certain conditions. Also, the required resistance for either winding may be incorporated therein, as by selecting a wire 'of smaller size or of a higher resistivity, but this practice is not generally recommended where the device is subject to nearly constant usage or where a winding thereof may be energized continuously for a considerable period, for a SO-watt heat dissipation at the electromagnet having the structure and size disclosed in Figs. 3 and 4 may occur only after an excessive temperature rise.

1f the structure of Figs. 3 and 4 is widened or is narrowed to accommodate a larger number or a smaller number of armatures A, both the volts per turn and the steady-state wattage should correspondingly be increased or decreased if the promptness of armature response is to be preserved unchanged.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

I claim:

1. In combination, an electromagnet, a Series of more than two similar armatures and means supporting them in operative relationship to the electromagnet for movement from a first position to a second position responsive to energization of the electromagnet, and circuit elements comprising a first energizing path through a winding of the electromagnet which includes (l) a circuit-closing device, (2) a current source having a potential per winding turn which is at least on the order of one ninth volt per turn, and (3) resistance-material which limits the steadystate wattage of the circuit path to a value which is at least on the order of fifty watts, means biasing the armatures to stand normally in the `said first position and to return thereto from the said second position when the said energizing path is opened unless restrained from so doing, the electromagnet being so related to the armatures in second position that the armatures are restrained therein by residual magnetism after the said energizing path is opened, and circuit elements comprising a second energizing path through a winding of the electromagnet which is of opposite magnetic polarity to the iirst said energizing path and includes (1) a circuit-closing device, (2) a current source having a potential per winding turn which is substantially higher than the current-source potential per winding turn of the said first energizing path and is at least on the order-of one quarter volt per turn, and (3) means for limiting the magnetomotive force developed by current flow in the path to a value in excess of that required to effectively neutralize the residual magnetism to thus permit the armatures to restore to the said iirst position and less than that required to cause the armatures to reoperate to the said second position.

2. A combination according to claim 1, wherein the said limiting means in the said second energizing path comprises contact means actuatable by one of the armatures 4upon moving out of its said second position.

3. A combination according to claim l, wherein the said limiting means in the said second energizing path comprises resistance-material which limits the steadystate Wattage of the circuit path to a value which is at least on the order of ii-fty Watts.

4. A combination according to claim 3, wherein the said limiting means in the said second energizing path further comprises contact means actuatable by one of the armatures upon moving out of its said second position.

5. In combination, an electromagnet, a series of similar armatures and means `supporting them in operative relationship to the electromagnet 'for movement `from a rst position to a second position responsive to operative energization of the electromagnet, means biasing the armatures to stand normally in their first position and to return thereto from their second position unless restrained magnetically from so doing, circuit elements comprising a magnetizing path which includes a circuit-closing means and includes a current source and a winding of the electromagnet having the number of its turns so related to the potential of the current source that there is a given potential per winding turn, the electromagnet remaining residually magnetized to restrain the armatures in second position after the energizing path is opened, and circuit elements comprising a demagnetizing path which includes a circuit closing means and includes a current source and a winding of the electromagnet having the number of its turns so related to the potential of the current source that there is a potential per winding turn which is higher than the said given potential, means Ifor limiting the magnetomotive force developed by current ow in the demagnetizing path to a value in excess of that required to permit the armatures to restore to the said rst position and less than that required to cause reversed magnetization suflicient to reoperate an armature to its second position.

6. A combination according to claim 5, wherein the said limiting means in the said demagnetizing path comprises contact means actuatable by one of the armatures upon restoration from its said second position.

7. In combination, an electromagnet, a series of more than two similar armatures and means supporting them in operative relationship to the electromagnet for operation from a first position to a second position responsive to energization of the electromagnet, and circuit elements comprising a magnetizing circuit path through a winding of the electromagnet which includes circuit-closing means and a current source, means biasing the armatures to stand normally in the said rst position and to return thereto from the said second position when the said energizing path is opened unless restrained from so doing, means for causing the electromagnet to restrain any operated armatures in second position by residual magnetism after the magnetizing circuit path is opened, and means for closing a demagnetizing circuit path through a winding of the electromagnet which is of opposite magnetic polarity to the magnetizing .path and which includes a current source and circuit-opening means controlled by the 'release of a single armature, the number of winding turns in the demagnetizing circuit path being sufficiently low in relation to the potential of the current source therein that, f upon the current-flow value being reached at which the most sensitive armature is magnetically released, the demagnetizing current reaches the Value at which the most insensitive armature o-f the series is magnetically released Ibefore ther first 'said' magnetically released rmature can restore, whereby the demagnetizing circuit path can be opened responsive to the restoration of any operated armature with the assurance that none 0f the armatures then remain magnetically unreleased.

References Cited inthe le of this patent Y UNITED STATES PATENTS smug c Mar. 21, '17944 Bellamy Ian. 23,1951 Mudd Apr. 1, 1952 Bellamy Apr. 7, 1953 Blair Sept. 18, 1956 

